1. Field of the Invention
The present invention concerns a method and a system for loading a load carrier, in particular pallets, with packages by means of a manipulator, in particular a robot.
2. Description of the Prior Art
It is know, for example, from EP 1 211 203 B1 and DE 10 2007 001 263 A1 to load pallets by means of a robot. While, automatic palletizing machines are conventionally used for loading homogeneous pallets with identical packages, industrial robots are advantageous for loading pallets with different packages in a predetermined sequence (i.e. the consignment). All types of packaged goods, in particular individual goods or goods bundles, are designated as packages.
In both cases, a packing pattern that describes the desired positions of the individual packages on the load carrier is initially generated by a palletizing algorithm or an operator.
Automatic or semi-automatic palletizing algorithms are based on a mathematical-physical model of a package stack on which an additional package is to be placed. The model can include, for example, dimensions, weights, pressure distributions and center of gravity positions of the packages and the like for the packages that are already contained in the package stack, and can map these features to a placement position for the additional package. From DE 10 2007 001 263 A1 it is also known to determine a stability criterion that describes a static or dynamic stability of the stacked packages on the basis of such a model of the package stack.
The model deviates from the real package stack, in particular due to deformations of the real packages under the load of other packages in the package stack and due to deviations between the theoretical desired position and the actual real position of packages. This can lead to different disadvantages. The real package stack is most often smaller than the model due to weight-dependent compressions of the lower packages. If the palletizing algorithm now continues based on the model, the package stack may not be built up to its maximum allowable height since the algorithm has already incorrectly determined this has occurred based on the model. In this case the available space is not optimally used, which increases transport or storage costs.
Moreover, the desired positions cannot be approached exactly due to the deviations between model and real package stack since this could lead to collisions with real packages at positions that are not correctly mapped in the model. A known solution is to drop the packages at a sufficient distance above their desired position, but this disadvantageously increases the position inaccuracy and thus the deviations between the model and real package stack. The alternative use of force-regulated approach strategies is not possible for softer packages, since the contact force required for regulation would lead to intolerable deformations of the soft packages.
If the stability of the package stack is assessed on the basis of a model that deviates too significantly from the real package stack, this can similarly lead to a failure (collapse) of a stack that is incorrectly assessed as stable, the early ending of a stack construction that is incorrectly assessed as being no longer stable, or a non-optimal packing pattern.